1. Field of the Invention
The present invention relates to an improved apparatus and method for operating and dimming fluorescent lamps and, in particular, to a method and apparatus to control the power delivered to a fluorescent lamp when receiving input power from a source utilizing a remote incandescent lamp dimming control.
2. Description of the Prior Art
Fluorescent lamps are conventional types of lighting devices. They are gas charged devices which provide illumination as a result of atomic excitation of a low-pressure gas, such as mercury, within a lamp envelope. The excitation of the mercury vapor atoms is provided by a pair of heater filament elements mounted within the lamp at opposite ends of the lamp envelope. These heater filament elements are coated with a material which emits electrons when excited by an electric current. In order to properly excite the mercury vapor atoms, the lamp is ignited or struck by a higher than normal voltage. Upon ignition of the lamp, the impedance of the lamp decreases and the voltage across the lamp drops to the operating level at a relatively constant current. The excited mercury vapor atoms emit invisible ultraviolet radiation which in turn excites a fluorescent lamp material, e.g., phosphor, that is deposited on an inside surface of the fluorescent lamp envelope, thus converting the invisible ultraviolet radiation to visible light. The fluorescent lamp coating material is selected to emit visible radiation over a wide spectrum of colors and intensities.
Fluorescent lamps have substantial advantages over conventional incandescent lamps. In particular, the fluorescent lamps are substantially more efficient and typically use 80 to 90% less electrical power than incandescent lamps for an equivalent light output. For this reason, fluorescent lamps have gained use in a wide range of power sensitive applications.
As is known to those skilled in the art, a ballast circuit is commonly disposed in electrical communication with the fluorescent lamp to provide the elevated voltage levels and the constant current required for fluorescent lamp illumination. Typical ballast circuits electrically connect the fluorescent lamp to line alternating current and convert this alternating current provided by the power transmission lines to the constant current an voltage levels required by the lamp.
To strike or light a fluorescent lamp, a high voltage level is required rather than high power. As a means of resolving the high power loss inherent in the design of electromagnetic ballasts, solid state designs have evolved. The present invention improves the efficiency of the electronic ballast and controls the dimming level through the incorporation of a novel series of feed forward and feedback control methods to tightly couple and control the power boost and Modified Self Resonant Load Driving Stages. In addition, many electronic fluorescent lamp ballasts are unable to work with conventional triac dimming switches as the leading edge phase control results in the ballast being unable to draw enough current to keep the triac firing. This is particularly true at lower dimming levels where sinking sufficient current to keep the triac firing and start the lamps is particularly difficult. The present invention resolves this problem.
Existing dimming ballast devices utilize a four wire arrangement to supply power and provide a dimming signal to control the lamps. This limits these ballasts to new installations. The present invention resolves this limitation and derives both power and dimming information from existing wiring when in communication with standard incandescent lamp 2-wire triac controlled dimming controls.
Additionally, at the end of a lamp's life-cycle, the voltage required to strike the lamp increases. This results in the lamp not lighting because the peak voltage required to strike the lamp cannot be provided by existing electromagnetic and electronic ballast designs. Also, low temperatures require a higher voltage to strike the lamp. This is due to the greater thermal gradient between the environmental temperature and that necessary to ignite the lamp. This limits the environmental operating range of current ballast designs, making them unusable at low wintertime temperatures. The present invention addresses the ability to extend the useful life of fluorescent lamps and provide improved cold starting capability.
Product safety considerations dictate that the circuit not operate when a lamp filament fails or the lamp is removed. Many designs require that when lamps are hot changed or fail that the circuit be reset. The present invention addresses these issues by providing a means to inhibit operation of the circuit when these conditions exist and immediately return to operating status when the fault condition is corrected, i.e., a functioning lamp is placed in communication with the ballast.